JP7457310B1 - Thin film solar cell and method for manufacturing thin film solar cell - Google Patents

Abstract

[Problem] To provide a thin-film solar cell capable of repairing damage caused by radiation, and a method for manufacturing the thin-film solar cell. [Solution] The p-type light absorbing layer of the thin-film solar cell has a first region and a second region obtained by dividing the p-type light absorbing layer into two equal parts. The p-type light absorbing layer contains Cu as a group I element and Ga and In as group III elements, and the average value of the atomic ratio C1 of Cu to group III elements in the first region is lower than the average value of the ratio C1 in the second region. The average value of the atomic ratio G1 of Ga to group III elements in the first region is lower than the average value of the ratio G1 in the second region, and the average value of the ratio G1 in the p-type light absorbing layer is 0.2 or more and 0.4 or less. The absolute value of the rate of change of the ratio G1 from the first electrode layer side to the second electrode layer side is maximum in the first region, and the ratio G1 in the p-type light absorbing layer tends to decrease from the first electrode layer side to the second electrode layer side in the first region. [Selected Figure] FIG.

Description

The present invention relates to a thin film solar cell and a method for manufacturing a thin film solar cell.

Thin film solar cells are one type of solar cells. Among the thin film solar cells, there is a CIS type thin film solar cell that uses a chalcopyrite structure I-III-VI group ₂ compound containing Cu, In, Ga, Se, S, etc. as a p-type light absorption layer. As shown in Non-Patent Document 1, CIS-based thin film solar cells have been actively studied academically. Furthermore, Patent Document 1 describes an atomic profile of a p-type light absorption layer aimed at improving the photoelectric conversion efficiency of a CIS thin film solar cell. Thin film solar cells are sometimes used in outer space, and Non-Patent Document 2 describes thin film solar cells used in outer space.

Patent No. 6297038

Physica Status Solidi. Rapid Research Letters, 2019, Vol.13, pp.1900415 Advanced Energy Materials, 2022, Vol.12, Issue 29, pp.2200125

Strong radiation exists in outer space, and thin-film solar cells placed in outer space are irradiated with strong radiation. Radiation causes defects in the light-absorbing layers within thin-film solar cells, degrading cell performance.

Therefore, an object of the present invention is to provide a long-life thin film solar cell that can withstand radiation and a method for manufacturing the thin film solar cell.

A thin-film solar cell according to an embodiment of the present disclosure includes a substrate, a first electrode layer provided on the substrate, a p-type light absorbing layer provided on the first electrode layer and containing a I-III-VI ₂ group compound, and an n-type second electrode layer provided on the p-type light absorbing layer, the p-type light absorbing layer having a first region on the second electrode layer side when the p-type light absorbing layer is divided into two equal parts in the depth direction of the p-type light absorbing layer, and a second region other than the first region. The p-type light absorbing layer includes Cu as a group I element and Ga and In as group III elements, and the average value of the atomic ratio of Cu to the group III elements in the first region is lower than the average value of the atomic ratio of Cu to the group III elements in the second region. The average value of the atomic ratio of Ga to the group III elements in the first region is lower than the average value of the atomic ratio of Ga to the group III elements in the second region, and the average value of the atomic ratio of Ga to the group III elements in the p-type light absorbing layer is 0.2 to 0.4. In the p-type light absorbing layer, the absolute value of the rate of change of the ratio of the number of atoms of Ga to the group III element from the first electrode layer side to the second electrode layer side is maximum in the first region, and the ratio of the number of atoms of Ga to the group III element in the p-type light absorbing layer tends to decrease from the first electrode layer side to the second electrode layer side in the first region.

A method for manufacturing a thin film solar cell according to one aspect of the present disclosure includes a first step of providing a first electrode layer on a substrate, and a p-type light containing a _group I-III-VI compound on the first electrode layer. A second step of providing an absorption layer; a third step of providing an n-type second electrode layer on the p-type light absorption layer; The p-type light absorption layer has a first region on the second electrode layer side when the p-type light absorption layer is divided into two, and a second region other than the first region, and the p-type light absorption layer contains a group I element. , contains Cu, and contains Ga and In as group III elements, and in the second step, the average value of the ratio of the number of atoms of Cu and group III elements in the first region is such that the average value of the ratio of the number of atoms of Cu and group III elements in the second region is lower than the average value of the ratio of the number of atoms, and the average value of the ratio of the number of atoms of Ga and group III elements in the first region is lower than the average value of the ratio of the number of atoms of Ga and group III elements in the second region; , the average value of the ratio of the number of atoms of Ga and group III elements in the p-type light absorption layer is 0.2 or more and 0.4 or less, and in the p-type light absorption layer, the second electrode layer is The absolute value of the rate of change in the ratio of the number of atoms of Ga and group III elements toward the side becomes maximum in the first region, and the ratio of the number of atoms of Ga and group III elements in the p-type light absorption layer increases in the first region. The p-type light absorption layer is provided so that the p-type light absorption layer tends to decrease in the region from the first electrode layer side to the second electrode layer side.

According to the present invention, it is possible to provide a long-life thin film solar cell that can withstand radiation and a method for manufacturing the thin film solar cell.

1 is a cross-sectional view of a thin-film solar cell according to an embodiment of the present invention. It is a figure showing the Cu profile in the p-type light absorption layer concerning this embodiment. It is a figure showing the Ga profile in the p-type light absorption layer concerning this embodiment. It is a figure which shows another example of Ga profile in the p-type light absorption layer based on this embodiment. It is a figure which shows another example of Ga profile in the p-type light absorption layer based on this embodiment. FIG. 2 is a cross-sectional view illustrating an example of a method for manufacturing a thin film solar cell according to the present embodiment. FIG. 2 is a cross-sectional view illustrating an example of a method for manufacturing a thin film solar cell according to the present embodiment. FIG. 2 is a cross-sectional view illustrating an example of a method for manufacturing a thin film solar cell according to the present embodiment. FIG. 2 is a cross-sectional view illustrating an example of a method for manufacturing a thin film solar cell according to the present embodiment. FIG. 2 is a cross-sectional view illustrating an example of a method for manufacturing a thin film solar cell according to the present embodiment. It is a figure explaining the recovery effect of the thin film solar cell concerning this embodiment. It is a figure explaining the recovery effect of the thin film solar cell concerning this embodiment. It is a figure explaining the recovery effect of the thin film solar cell concerning this embodiment. 1A to 1C are diagrams illustrating the recovery effect of a thin-film solar cell according to an embodiment of the present invention. It is a figure which compares the recovery effect of the thin film solar cell based on this embodiment, and other thin film solar cells.

Preferred embodiments of the present invention will be described with reference to the accompanying drawings. In addition, in each figure, those with the same reference numerals have the same or similar configurations.

FIG. 1 shows a cross-sectional view of a thin film solar cell 100 according to this embodiment. The thin film solar cell 100 has a substrate 101 , a first electrode layer 102 , a p-type light absorption layer 103 , an electron transport layer 104 , a second electrode layer 105 , and a grid electrode 106 . The thin film solar cell 100 receives light from the grid electrode 106 side and generates electricity.

The substrate 101 may be, for example, a glass substrate such as soda lime glass or low-alkali glass, a metal substrate such as a stainless steel plate, or a polyimide resin substrate. The first electrode layer 102 may be, for example, a metal conductive layer disposed on the substrate 101 and made of a metal such as Mo, Cr, or Ti. The film thickness of the first electrode layer 102 may be, for example, 200 to 800 nm.

The p-type light absorbing layer 103 is disposed on the first electrode layer 102, for example, and is formed of a I-III-VI ₂ group compound. The p-type light absorbing layer 103 contains Cu as a group I element, Ga and In as group III elements, and Se and S as group VI elements. The thickness of the p-type light absorbing layer 103 can be, for example, 1 to 3 μm.

The p-type light absorption layer 103 has a first region R1 on the second electrode layer 105 side and a first region R1 on the second electrode layer 105 side when the p-type light absorption layer 103 is divided into two in the depth direction of the p-type light absorption layer 103. Unlike the other regions, it has a second region R2 on the first electrode layer 102 side. Further, the first region R1 is different from the third region R3 on the second electrode layer 105 side when the first region R1 is divided into two in the depth direction of the p-type light absorption layer 103. , has a second region R2 or a fourth region R4 on the first electrode layer 102 side.

The electron transport layer 104 is disposed on the p-type light absorption layer 103, for example, and may be made of Zn(O, S, OH) _x , which has n-type conductivity, is transparent, and has high resistance. The electron transport layer 104 can be formed to have a thickness of 20 to 150 nm, for example. Further, the electron transport layer 104 is made of, for example, a II-VI group compound semiconductor thin film such as CdS, ZnS, or ZnO, or Zn(O,S) _x which is a mixed crystal thereof, and a specific example is In ₂ O. It can also be formed using an In-based compound semiconductor thin film such as In ₃ , In ₂ S ₃ , In(O, S, OH) _x .

The second electrode layer 105 is disposed on the electron transport layer 104, and may be made of, for example, ZnO:B, which has n-type conductivity, a wide band gap, is transparent, and has a low resistance. The second electrode layer 105 may be formed as a transparent conductive film having a thickness of, for example, 0.1 to 1.5 μm. The second electrode layer 105 may also be formed as a transparent conductive film made of ZnO:Al, ZnO:Ga, and ITO.

The grid electrode 106 is, for example, an electrode placed on the second electrode layer 105 and provided for extracting electricity from the second electrode layer 105. The grid electrode 106 is made of a conductive material, and for example, a metal material, an alloy material, a transparent conductive material, or the like can be used.

<Example>
Next, the ratio of the number of atoms of Cu to group III elements (C1) and the ratio of the number of atoms of Ga to group III element (G1) in the p-type light absorption layer 103 of the thin film solar cell 100 according to the present embodiment will be explained. . The inventor manufactured three thin film solar cells 100 (A to C) according to the present embodiment, and explained the ratios C1 and G1 measured for the three examples with reference to FIGS. 2 to 5. do. The number of atoms is measured, for example, by measuring the cross section of the light absorption layer by energy dispersive X-ray spectroscopy using a scanning electron microscope.

FIG. 2 shows an example of the ratio C1 of the number of atoms of Cu and group III elements in the p-type light absorption layer 103 in Example A of the thin-film solar cell 100. The horizontal axis in FIG. 2 is the depth from the surface of the p-type light absorption layer 103 on the second electrode layer 105 side. The horizontal axis is also common in FIGS. 3 to 5. The ratio C1 of the number of atoms of Cu and group III element is calculated as the ratio of (number of atoms of Cu)/(number of atoms of group III element). Group III elements are, for example, In and Ga.

The ratio C1 of the entire p-type light absorption layer 103 is lower than 1.0. In the example of FIG. 2, the average value of the ratio C1 over the entire layer is 0.91. When the ratio C1 is 1.0 or more, the photoelectric conversion efficiency may decrease. On the other hand, the ratio C1 is preferably larger than 0.80 from the viewpoint of forming a p-type light absorption layer with an appropriate carrier concentration.

Furthermore, in the p-type light absorption layer 103, the average value of the ratio C1 in the first region R1 is lower than the average value of the ratio C1 in the second region R2. In the example of FIG. 2, the average value of the ratio C1 in the first region R1 is 0.89, and the average value of the ratio C1 in the second region R2 is 0.94.

In this way, by lowering the ratio C1 on the surface on the second electrode layer 105 side, the thin film solar cell 100 can repair damage caused by radiation.

Specifically, it is known that radiation causes defects in Cu in the crystal structure of the p-type light absorption layer 103. Defects include antisite defects that are generated when In and Ga, which are group III elements, are placed in Cu vacancies generated by radiation. Antisite defects greatly deteriorate electrical properties. Antisite defects are passivated by being modified with other Cu vacancies, and in this case, deterioration of electrical properties is reduced. Furthermore, it is known that Cu vacancies can transition within the p-type light absorption layer even with relatively weak external energy such as light irradiation or heating, and this transition is used to promote the modification of antisite defects by Cu vacancies. As a result, even if the thin film solar cell 100 is damaged, it can self-repair, and as a result, damage caused by radiation can be repaired.

In the p-type light absorption layer 103, by lowering the ratio of the number of atoms of Cu and group III elements on the surface on the second electrode layer 105 side, it is possible to increase the number of Cu vacancies that cause defect repair. This makes it possible for the thin film solar cell 100 to repair damage caused by radiation.

Figures 3 to 5 show an example of the ratio G1 of the number of atoms of Ga to group III elements in the p-type light absorbing layer 103 in Examples A to C. The ratio G1 of the number of atoms of Ga to group III elements is calculated as the ratio (number of Ga atoms)/(number of group III elements).

In the p-type light absorption layer 103, the average value of the ratio G1 in the first region R1 is lower than the average value of the ratio G1 in the second region R2. In the example of FIG. 3, the average value of the ratio G1 in the first region R1 in Example A is 0.13, and the average value of the ratio G1 in the second region is 0.45. In the example of FIG. 4, the average value of the ratio G1 in the first region R1 in Example B is 0.15, and the average value of the ratio G1 in the second region is 0.42. In the example of FIG. 5, the average value of the ratio G1 in the first region R1 in Example C is 0.09, and the average value of the ratio G1 in the second region is 0.48.

In the p-type light absorption layer 103, the average value of the ratio G1 in the p-type light absorption layer 103 is 0.2 or more and 0.4 or less. 3, FIG. 4, and FIG. 5 show a case where the average value of the ratio G1 in the entire p-type light absorption layer 103 is 0.29. The photoelectric conversion efficiency can be increased by setting the average value of the ratio G1 to 0.2 or more and 0.4 or less.

In the p-type light absorption layer 103, the absolute value of the rate of change of the ratio G1 from the first electrode layer 102 side to the second electrode layer 105 side is maximum in the first region R1. In the example of FIG. 3, the absolute value of the rate of change of the ratio G1 takes a maximum value of 74.6% in the first region R1. In the example of FIG. 4, the absolute value of the rate of change of the ratio G1 takes a maximum value of 52.7% in the first region R1. In the example of FIG. 5, the absolute value of the rate of change of the ratio G1 takes a maximum value of 70.4% in the first region R1. More specifically, in all of FIGS. 3 to 5, the absolute value of the rate of change of the ratio G1 is maximum in the fourth region R4 within the first region R1.

In this way, by setting the position where the absolute value of the rate of change of the ratio G1 is maximum in the first region R1, which is the region on the second electrode layer 105 side, the conduction band of the p-type light absorption layer 103 is Electron transfer to the surface on the second electrode layer 105 side can be promoted by utilizing the band slope of .

The ratio G1 in the p-type light absorption layer 103 tends to decrease from the first electrode layer 102 side to the second electrode layer 105 side in the first region R1. This tendency is commonly shown in each of FIGS. 3, 4, and 5.

In the p-type light absorption layer 103, the ratio G1 in the third region R3 is preferably 0.15 or less. More preferably, the ratio G1 is, for example, 0.13 or less. In the example of FIG. 3, the maximum value of the ratio G1 in the third region R3 is 0.10. In the example of FIG. 4, the maximum value of the ratio G1 in the third region R3 is 0.13. In the example of FIG. 5, the maximum value of the ratio G1 in the third region R3 is 0.06. Further, in the first region R1, in a region at a depth of up to 300 nm from the surface on the second electrode layer 105 side, the ratio G1 is 0.1 or less.

In this way, by adjusting the ratio G1 of the entire p-type light absorption layer 103 and the ratio G1 of the surface on the second electrode layer 105 side, the thin film solar cell 100 can be repaired from damage caused by radiation. Among the above-mentioned antisite defects, an antisite defect in which Ga is arranged in a Cu vacancy has a characteristic that it is difficult to self-repair by light irradiation or heating. As in the p-type light absorption layer 103, by lowering the ratio of the number of atoms of Ga and group III elements on the surface on the second electrode layer 105 side, Ga, which causes defects that are difficult to self-repair, is reduced. Therefore, the occurrence of defects can be suppressed and the thin film solar cell 100 can be repaired from damage caused by radiation.

Finally, the p-type light absorption layer 103 contains S as a group VI element. More specifically, S may be included in the first region R1. Thereby, the bandgap of the p-type light absorption layer 103 can be adjusted and the photoelectric conversion efficiency can be increased. In particular, by including S in the first region R1 with a reduced Ga ratio, it is possible to improve the photoelectric conversion efficiency while making it possible to repair damage caused by radiation.

<Manufacturing method>
Next, a method for manufacturing thin film solar cell 100 will be described with reference to FIGS. 6A to 6E.

First, as shown in FIG. 6A, a first electrode layer 102 is formed on a substrate 101. The thickness of the first electrode layer 102 may be, for example, 200 to 800 nm. The first electrode layer 102 is formed using, for example, Mo as a material by DC sputtering. The film forming conditions for the DC sputtering method may be a film forming pressure of 0.5 to 2.5 Pa and an applied power of 1.0 to 3.0 W/cm ² .

Next, as shown in FIG. 6B, a p-type light absorption layer 103 containing a _group I-III-VI compound is formed on the first electrode layer 102.

Examples of methods for forming the p-type light absorption layer 13 include (1) forming a metal precursor film of a group I element and a group III element, and forming a compound of the metal precursor film and a group VI element; 2) A method of forming a film of a group I element, a group III element, and a group VI element using a vapor deposition method can be mentioned.

First, a case will be described in which the p-type light absorption layer 103 is formed using method (1). In method (1), a precursor film containing Ga and Cu is formed on the first electrode layer 102, then a precursor film containing In is formed, and then a precursor film containing Ga and Cu and In is formed. A compound of the precursor film containing the group VI elements (Se and S) is formed. Regarding Cu, which is a group I element, as described above, a precursor film containing a mixed crystal of Ga and Cu may be formed, and a precursor film containing Cu may be laminated on a precursor film containing Ga. You may. The Cu concentration on the surface of the precursor film is controlled using the Se--S concentration in the reaction gas.

Each precursor film may be formed using a known film forming technique such as sputtering, for example. In this way, the p-type light absorption layer 103 having the atomic profile described with reference to FIGS. 2 to 5 can be formed.

In addition, the number of atoms of Ga and group III elements on the surface can be increased by shortening the heat treatment time for forming compounds with group VI elements and by adding alkaline compounds (e.g., addition into the precursor film or diffusion from the substrate). The ratio G1 can be lowered.

Note that the ratio C1 of the number of atoms of Cu and group III elements in the entire p-type light absorption layer 103 can be determined by controlling the number of atoms of Cu and group III elements in the stacked precursor film, for example, by controlling the number of atoms of Cu and group III elements in the stacked precursor film. It can be adjusted by changing the ratio of the film thickness between the film and the In precursor film, or the ratio of the film thickness between the Cu--Ga precursor film and the Cu precursor film.

Next, a case will be described in which the p-type light absorption layer 103 is formed by method (2). In method (2), when group I elements, group III elements, and group VI elements are vapor-deposited on the first electrode layer 102 as vapor deposition sources, Ga is vapor-deposited as the vapor-deposition of the group-III elements before the vapor deposition of In. By doing so, a semiconductor layer having a chalcopyrite structure is formed, and a p-type light absorption layer 103 is formed. In this way, the p-type light absorption layer 103 having the atomic profile described with reference to FIGS. 2 to 5 may be formed. In addition, the ratio of the number of atoms of Ga and group III elements on the surface can be improved by shortening the heat treatment time for vapor deposition of group VI elements and by adding alkali compounds (evaporation using an alkali compound as a vapor deposition source, diffusion of alkali metals from the substrate). G1 can be lowered.

Cu, which is a Group I element, may be further deposited as a deposited film containing Cu and Ga or In, or as a deposition source containing Cu and S or Se to form a p-type light absorption layer.

Se or S, which is a group VI element, may be deposited as a Se film, an S film, or a film containing Se and S.

For example, the p-type light absorption layer 103 is formed by first depositing Ga and Se on the first electrode layer 102, or depositing Ga, In, and Se, and then depositing Cu, Se, and S. Finally, it is formed by depositing In, Se, and S. The heat generated when each element is vapor-deposited forms a compound of Cu, Se or S, and In and Ga. Further, after each element is vapor-deposited, heat treatment may be performed to form a compound of Cu, Se or S, and In or Ga. For example, a method such as a multi-component simultaneous vapor deposition method can be used for vapor deposition.

Further, on the first electrode layer 102, Cu and Ga (or a CuGa compound) are first vapor-deposited, then Cu and In (or a CuIn compound) are vapor-deposited, and then Se, S, and In are vapor-deposited. (or an InSeS compound) may be deposited to form the p-type light absorption layer 103. The heat generated when In(Se, S) is deposited forms a compound of Cu, Se or S, and In, Ga. Further, after depositing In(Se, S), heat treatment may be performed to form a compound of Cu, Se or S, and In and Ga.

Alternatively, the p-type light absorbing layer 103 may be formed by first evaporating Cu and Ga (or a CuGa compound) on the first electrode layer 102, then evaporating Cu and In (or a CuIn compound), and then evaporating Se and S (or a SeS compound). A compound of Cu, Se or S, and In and Ga is formed by the heat generated when Se-S is evaporated. Alternatively, after the evaporation of Se-S, a heat treatment may be performed to form a compound of Cu, Se or S, and In and Ga. This concludes the description of the process of forming the p-type light absorbing layer 103 using method (2).

Next, as shown in FIG. 6C, an electron transport layer 104 is formed on the p-type light absorption layer 103. The electron transport layer 104 can be formed by a solution growth method, MOCVD method, ALD method, vapor deposition method, or sputtering method. Next, as shown in FIG. 6D, a second electrode layer 105 is formed on the electron transport layer 104. The second electrode layer 105 may be formed by sputtering or MOCVD. Next, as shown in FIG. 6E, a grid electrode 106 is formed on the second electrode layer 105. The grid electrode 106 may be formed, for example, by a vapor deposition method or by printing a paste-like conductive material on the second electrode layer 105.

<Self-healing effect>
The self-healing effect of thin film solar cell 100 will be described with reference to FIGS. 7A to 7D. 7A to 7D show the storage rate of the photoelectric conversion efficiency of the thin-film solar cell 100 (FIG. 7A) and the storage rate of the open-circuit voltage V _oc of the thin-film solar cell 100 when the thin-film solar cell 100 is irradiated with a proton beam. (FIG. 7B), the storage rate of the short circuit current density _Jsc of the thin film solar cell 100 (FIG. 7C), and the storage rate of the fill factor (FF) of the thin film solar cell 100 (FIG. 7D) are shown, respectively. Each data in FIGS. 7A to 7D is an average value of data obtained from a plurality of thin film solar cells 100 including the thin film solar cells 100 of Examples A, B, and C.

The horizontal axis in FIGS. 7A to 7D is proton fluence, which indicates the number of proton beam particles per unit area. In FIGS. 7A to 7D, each storage rate when irradiated with a 300 keV proton beam is shown by a solid line, and each storage rate when irradiated with a 3 MeV proton beam is shown by a broken line. The preservation rate is the ratio of the value after irradiation to the value before irradiation. In addition, in the examples of FIGS. 7A to 7D, each case where light irradiation (Light Soaking: LS) and heat light irradiation (Heat Light Soaking: HLS) are performed for self-repair of the thin film solar cell 100 after irradiation is shown. The retention rate is indicated. The light irradiation or thermal light irradiation promotes the movement of Cu defects within the p-type light absorption layer 103, modifies antisite defects, and recovers the performance of the thin film solar cell 100. Moreover, for comparison, each storage rate in the case where no light irradiation or thermal light irradiation is performed is shown.

As commonly shown in FIGS. 7A to 7D, even when the performance of the thin-film solar cell 100 is degraded by being irradiated with the proton beam, for example, as shown in the case without repair, Each characteristic is greatly recovered by light irradiation or thermal light irradiation. The recovery of such characteristics is considered to be due to the fact that the p-type light absorption layer 103 has the atomic profile described with reference to FIGS. 2 to 5.

In the example of Figures 7A to 7D, thermal irradiation was performed by irradiating light at a temperature of 150°C for one hour. This corresponds to approximately 16 to 69 days at a temperature of 60°C. Therefore, the thin-film solar cell 100 can perform sufficient self-repair even in an actual space environment.

FIG. 8 shows the preservation rate of photoelectric conversion efficiency when the thin film solar cell 100 according to this embodiment and other thin film solar cells are each irradiated with a 300 keV proton beam and self-repaired by thermal irradiation. . The data of the thin film solar cell 100 in FIG. 8 is an average value of data from a plurality of thin film solar cells 100 including the thin film solar cells 100 of Examples A, B, and C. In FIG. 8, the storage rate RF1 of the photoelectric conversion efficiency of the thin-film solar cell 100, the storage rate RF2 of the photoelectric conversion efficiency of the thin-film solar cell described in Non-Patent Document 1, and the storage rate RF2 of the photoelectric conversion efficiency of the thin-film solar cell described in Non-Patent Document 2 (GaAs-based ) is shown is the storage rate RF3 of the photoelectric conversion efficiency of the thin film solar cell. Thin film solar cell 100 has been shown to have a higher self-healing effect than other thin film solar cells.

In general thin-film solar cells placed in space, in order to suppress deterioration of cell performance, protective measures such as a cover glass that protects the light absorption layer of the thin-film solar cell are bonded to the thin-film solar cell using an adhesive. is attached to. However, space-use cover glasses and adhesives are very expensive, and furthermore, the use of cover glasses and adhesives increases the weight of the entire power generation device, which is undesirable. Therefore, by making the thin film solar cell itself capable of sufficient self-repair like the thin film solar cell 100, there is no need to use a cover glass or an adhesive. Thereby, the battery module including the thin film solar cell 100 can be made lightweight, and the cost for launching and the cost due to the number of parts can be reduced. Furthermore, since the thin film solar cell 100 can self-repair damage caused by radiation, it can be used as a long-life battery in outer space or in the atmosphere above the stratosphere. Further, since the thin film solar cell 100 has radiation resistance, it can be used as a cell with a longer life than conventional thin film solar cells even in a radiation environment. Furthermore, it can be used as a battery with a longer life even in the troposphere, where the amount of radiation is lower than in outer space. For example, it can be attached to the surfaces (roofs, windows, walls, etc.) of buildings, moving objects, aircraft, etc., and used as long-life power generation devices.

The thin film solar cell 100 according to this embodiment has been described above. The thin film solar cell 100 includes a substrate 101, a first electrode layer 102 provided on the substrate 101, and a p-type light absorption layer 103 provided on the first electrode layer 102 and containing a _group I-III-VI compound. and an n-type second electrode layer 105 provided on the p-type light absorption layer 103, and the p-type light absorption layer 103 absorbs p-type light in the depth direction of the p-type light absorption layer 103. It has a first region R1 on the second electrode layer 105 side when the absorbing layer 103 is divided into two, and a second region R2 other than the first region R1. The p-type light absorption layer 103 contains Cu as a group I element, Ga and In as group III elements, and the average value of the ratio of the number of atoms of Cu and group III elements in the first region R1 is the second It is lower than the average value of the ratio of the number of atoms of Cu and group III elements in region R2. The average value of the ratio of the number of atoms of Ga to the group III element in the first region R1 is lower than the average value of the ratio of the number of atoms of Ga to the group III element in the second region R2, and the Ga The average ratio of the number of atoms of the group III element and the group III element is 0.2 or more and 0.4 or less. In the p-type light absorption layer 103, the absolute value of the rate of change in the ratio of the number of atoms of Ga and group III elements from the first electrode layer 102 side to the second electrode layer 105 side is maximum in the first region R1. , the ratio of the number of atoms of Ga and group III elements in the p-type light absorption layer tends to decrease from the first electrode layer 102 side to the second electrode layer 105 side in the first region R1.

In the p-type light absorption layer 103, the amount of Cu vacancies that repair defects caused by radiation can be increased on the second electrode layer 105 side, so that the thin film solar cell 100 can repair damage caused by radiation. can. In addition, by lowering the ratio of the number of atoms of Ga and group III elements on the surface on the second electrode layer 105 side, it is possible to reduce the amount of Ga, which causes defects that are difficult to self-repair. The thin film solar cell 100 can easily repair damage caused by radiation. By locating the position where the absolute value of the rate of change in the ratio of the number of atoms of Ga and group III elements is maximum in the first region R1, the band slope of the conduction band of the p-type light absorption layer 103 is utilized. Electron transfer to the surface on the second electrode layer 105 side can be promoted, and electrical characteristics can be improved. These factors allow the thin film solar cell 100 to repair damage caused by radiation.

The p-type light absorbing layer 103 may also contain S as a group VI element, which can adjust the band gap of the p-type light absorbing layer 103 and increase the photoelectric conversion efficiency. In particular, by including S in the first region R1, which has a reduced Ga ratio, it is possible to increase the photoelectric conversion efficiency while making it possible to repair damage caused by radiation.

The embodiments described above are intended to facilitate understanding of the present invention, and are not intended to be interpreted as limiting the present invention. Each element included in the embodiment, as well as its arrangement, material, conditions, shape, size, etc., are not limited to those illustrated, and can be changed as appropriate. Further, it is possible to partially replace or combine the structures shown in different embodiments.

DESCRIPTION OF SYMBOLS 100... Thin film solar cell, 101... Substrate, 102... First electrode layer, 103... P-type light absorption layer 103, 104... Electron transport layer 104, 105... Second electrode layer, 106... Grid electrode

Claims (4)

A substrate and
a first electrode layer provided on the substrate;
a p-type light absorption layer provided on the first electrode layer and containing a Group I-III-VI2 compound;
an n-type second electrode layer provided on the p-type light absorption layer,
The p-type light absorption layer includes a first region on the second electrode layer side when the p-type light absorption layer is divided into two in the depth direction of the p-type light absorption layer, and the first region. and a second region other than
The first region has a third region on the second electrode layer side when the first region is divided into two in the depth direction, and a fourth region other than the third region,
The p-type light absorption layer is
Contains Cu as a group I element,
Group III elements include Ga and In,
The average value of the ratio of the number of atoms of Cu and the group III element in the first region is lower than the average value of the ratio of the number of atoms of Cu and the group III element in the second region,
The average value of the ratio of the number of atoms of Ga to the group III element in the first region is lower than the average value of the ratio of the number of atoms of Ga to the group III element in the second region,
The average value of the ratio of the number of atoms of Ga and group III elements in the p-type light absorption layer is 0.2 or more and 0.4 or less,
In the p-type light absorption layer, the absolute value of the rate of change in the ratio of the number of atoms of Ga and group III elements from the first electrode layer side to the second electrode layer side is maximum in the fourth region. ,
The ratio of the number of atoms of Ga and group III elements in the p-type light absorption layer tends to decrease from the first electrode layer side to the second electrode layer side in the first region ,
A thin film solar cell , wherein the ratio of the number of atoms of Ga and group III element in the third region is 0.15 or less . The thin-film solar cell according to claim 1 ,
The thin-film solar cell, wherein the p-type light absorbing layer contains S as a Group VI element. The thin-film solar cell according to claim 2,
The thin-film solar cell, wherein the S is included in the first region. A first step of providing a first electrode layer on the substrate;
a second step of providing a p-type light absorption layer containing a group I-III-VI compound on the first electrode layer;
a third step of providing an n-type second electrode layer on the p-type light absorption layer,
The p-type light absorption layer includes a first region on the second electrode layer side when the p-type light absorption layer is divided into two in the depth direction of the p-type light absorption layer, and the first region. and a second region other than
The first region has a third region on the second electrode layer side when the first region is divided into two in the depth direction, and a fourth region other than the third region,

The p-type light absorption layer is
Contains Cu as a group I element,
Group III elements include Ga and In,
The second step is
The average value of the ratio of the number of atoms of Cu and the group III element in the first region is lower than the average value of the ratio of the number of atoms of Cu and the group III element in the second region,
The average value of the ratio of the number of atoms of Ga to the group III element in the first region is lower than the average value of the ratio of the number of atoms of Ga to the group III element in the second region,
The average value of the ratio of the number of atoms of Ga and group III elements in the p-type light absorption layer is 0.2 or more and 0.4 or less,
In the p-type light absorption layer, the absolute value of the rate of change in the ratio of the number of atoms of Ga and group III elements from the first electrode layer side to the second electrode layer side is maximum in the fourth region. ,
The ratio of the number of atoms of Ga and group III elements in the p-type light absorption layer tends to decrease from the first electrode layer side to the second electrode layer side in the first region ,
A method for manufacturing a thin film solar cell , wherein the ratio of the number of atoms of Ga to group III element in the third region is 0.15 or less .

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